UTF32Encoding.GetMaxCharCount(Int32) Method
Important
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Calculates the maximum number of characters produced by decoding the specified number of bytes.
public:
override int GetMaxCharCount(int byteCount);C#
public override int GetMaxCharCount(int byteCount);override this.GetMaxCharCount : int -> intPublic Overrides Function GetMaxCharCount (byteCount As Integer) As Integer- byteCount
- Int32
The number of bytes to decode.
The maximum number of characters produced by decoding the specified number of bytes.
byteCount is less than zero.
-or-
The resulting number of bytes is greater than the maximum number that can be returned as an integer.
A fallback occurred (for more information, see Character Encoding in .NET)
-and-
DecoderFallback is set to DecoderExceptionFallback.
The following example encodes a string into an array of bytes, and then decodes the bytes into an array of characters.
using namespace System;
using namespace System::Text;
void PrintCountsAndChars( array<Byte>^bytes, Encoding^ enc );
int main()
{
// Create two instances of UTF32Encoding: one with little-endian byte order and one with big-endian byte order.
UTF32Encoding^ u32LE = gcnew UTF32Encoding( false,true,true );
UTF32Encoding^ u32BE = gcnew UTF32Encoding( true,true,true );
// Create byte arrays from the same string containing the following characters:
// Latin Small Letter Z (U+007A)
// Latin Small Letter A (U+0061)
// Combining Breve (U+0306)
// Latin Small Letter AE With Acute (U+01FD)
// Greek Small Letter Beta (U+03B2)
String^ myStr = L"za\u0306\u01FD\u03B2\xD8FF\xDCFF";
// barrBE uses the big-endian byte order.
array<Byte>^barrBE = gcnew array<Byte>(u32BE->GetByteCount( myStr ));
u32BE->GetBytes( myStr, 0, myStr->Length, barrBE, 0 );
// barrLE uses the little-endian byte order.
array<Byte>^barrLE = gcnew array<Byte>(u32LE->GetByteCount( myStr ));
u32LE->GetBytes( myStr, 0, myStr->Length, barrLE, 0 );
// Get the char counts and decode the byte arrays.
Console::Write( "BE array with BE encoding : " );
PrintCountsAndChars( barrBE, u32BE );
Console::Write( "LE array with LE encoding : " );
PrintCountsAndChars( barrLE, u32LE );
// Decode the byte arrays using an encoding with a different byte order.
Console::Write( "BE array with LE encoding : " );
try
{
PrintCountsAndChars( barrBE, u32LE );
}
catch ( System::ArgumentException^ e )
{
Console::WriteLine( e->Message );
}
Console::Write( "LE array with BE encoding : " );
try
{
PrintCountsAndChars( barrLE, u32BE );
}
catch ( System::ArgumentException^ e )
{
Console::WriteLine( e->Message );
}
}
void PrintCountsAndChars( array<Byte>^bytes, Encoding^ enc )
{
// Display the name of the encoding used.
Console::Write( "{0,-25} :", enc );
// Display the exact character count.
int iCC = enc->GetCharCount( bytes );
Console::Write( " {0,-3}", iCC );
// Display the maximum character count.
int iMCC = enc->GetMaxCharCount( bytes->Length );
Console::Write( " {0,-3} :", iMCC );
// Decode the bytes and display the characters.
array<Char>^chars = gcnew array<Char>(iCC);
enc->GetChars( bytes, 0, bytes->Length, chars, 0 );
Console::WriteLine( chars );
}
/*
This code produces the following output. The question marks take the place of characters that cannot be displayed at the console.
BE array with BE encoding : System.Text.UTF32Encoding : 7 14 :za??�?
LE array with LE encoding : System.Text.UTF32Encoding : 7 14 :za??�?
BE array with LE encoding : System.Text.UTF32Encoding :Invalid byte was found at byte index 3.
LE array with BE encoding : System.Text.UTF32Encoding :Invalid byte was found at byte index 3.
*/
C#
using System;
using System.Text;
public class SamplesUTF32Encoding {
public static void Main() {
// Create two instances of UTF32Encoding: one with little-endian byte order and one with big-endian byte order.
UTF32Encoding u32LE = new UTF32Encoding( false, true, true );
UTF32Encoding u32BE = new UTF32Encoding( true, true, true );
// Create byte arrays from the same string containing the following characters:
// Latin Small Letter Z (U+007A)
// Latin Small Letter A (U+0061)
// Combining Breve (U+0306)
// Latin Small Letter AE With Acute (U+01FD)
// Greek Small Letter Beta (U+03B2)
// a high-surrogate value (U+D8FF)
// a low-surrogate value (U+DCFF)
String myStr = "za\u0306\u01FD\u03B2\uD8FF\uDCFF";
// barrBE uses the big-endian byte order.
byte[] barrBE = new byte[u32BE.GetByteCount( myStr )];
u32BE.GetBytes( myStr, 0, myStr.Length, barrBE, 0 );
// barrLE uses the little-endian byte order.
byte[] barrLE = new byte[u32LE.GetByteCount( myStr )];
u32LE.GetBytes( myStr, 0, myStr.Length, barrLE, 0 );
// Get the char counts and decode the byte arrays.
Console.Write( "BE array with BE encoding : " );
PrintCountsAndChars( barrBE, u32BE );
Console.Write( "LE array with LE encoding : " );
PrintCountsAndChars( barrLE, u32LE );
// Decode the byte arrays using an encoding with a different byte order.
Console.Write( "BE array with LE encoding : " );
try {
PrintCountsAndChars( barrBE, u32LE );
}
catch ( System.ArgumentException e ) {
Console.WriteLine( e.Message );
}
Console.Write( "LE array with BE encoding : " );
try {
PrintCountsAndChars( barrLE, u32BE );
}
catch ( System.ArgumentException e ) {
Console.WriteLine( e.Message );
}
}
public static void PrintCountsAndChars( byte[] bytes, Encoding enc ) {
// Display the name of the encoding used.
Console.Write( "{0,-25} :", enc.ToString() );
// Display the exact character count.
int iCC = enc.GetCharCount( bytes );
Console.Write( " {0,-3}", iCC );
// Display the maximum character count.
int iMCC = enc.GetMaxCharCount( bytes.Length );
Console.Write( " {0,-3} :", iMCC );
// Decode the bytes and display the characters.
char[] chars = new char[iCC];
enc.GetChars( bytes, 0, bytes.Length, chars, 0 );
Console.WriteLine( chars );
}
}
Imports System.Text
Public Class SamplesUTF32Encoding
Public Shared Sub Main()
' Create two instances of UTF32Encoding: one with little-endian byte order and one with big-endian byte order.
Dim u32LE As New UTF32Encoding(False, True, True)
Dim u32BE As New UTF32Encoding(True, True, True)
' Create byte arrays from the same string containing the following characters:
' Latin Small Letter Z (U+007A)
' Latin Small Letter A (U+0061)
' Combining Breve (U+0306)
' Latin Small Letter AE With Acute (U+01FD)
' Greek Small Letter Beta (U+03B2)
' a high-surrogate value (U+D8FF)
' a low-surrogate value (U+DCFF)
Dim myStr As String = "za" & ChrW(&H0306) & ChrW(&H01FD) & ChrW(&H03B2) & ChrW(&HD8FF) & ChrW(&HDCFF)
' barrBE uses the big-endian byte order.
' NOTE: In Visual Basic, arrays contain one extra element by default.
' The following line creates an array with the exact number of elements required.
Dim barrBE(u32BE.GetByteCount(myStr) - 1) As Byte
u32BE.GetBytes(myStr, 0, myStr.Length, barrBE, 0)
' barrLE uses the little-endian byte order.
' NOTE: In Visual Basic, arrays contain one extra element by default.
' The following line creates an array with the exact number of elements required.
Dim barrLE(u32LE.GetByteCount(myStr) - 1) As Byte
u32LE.GetBytes(myStr, 0, myStr.Length, barrLE, 0)
' Get the char counts and decode the byte arrays.
Console.Write("BE array with BE encoding : ")
PrintCountsAndChars(barrBE, u32BE)
Console.Write("LE array with LE encoding : ")
PrintCountsAndChars(barrLE, u32LE)
' Decode the byte arrays using an encoding with a different byte order.
Console.Write("BE array with LE encoding : ")
Try
PrintCountsAndChars(barrBE, u32LE)
Catch e As System.ArgumentException
Console.WriteLine(e.Message)
End Try
Console.Write("LE array with BE encoding : ")
Try
PrintCountsAndChars(barrLE, u32BE)
Catch e As System.ArgumentException
Console.WriteLine(e.Message)
End Try
End Sub
Public Shared Sub PrintCountsAndChars(bytes() As Byte, enc As Encoding)
' Display the name of the encoding used.
Console.Write("{0,-25} :", enc.ToString())
' Display the exact character count.
Dim iCC As Integer = enc.GetCharCount(bytes)
Console.Write(" {0,-3}", iCC)
' Display the maximum character count.
Dim iMCC As Integer = enc.GetMaxCharCount(bytes.Length)
Console.Write(" {0,-3} :", iMCC)
' Decode the bytes and display the characters.
Dim chars(iCC) As Char
enc.GetChars(bytes, 0, bytes.Length, chars, 0)
Console.WriteLine(chars)
End Sub
End Class
To calculate the exact array size required by GetChars to store the resulting characters, you call the GetCharCount method. To calculate the maximum array size, you call the GetMaxCharCount method. The GetCharCount method generally allocates less memory, while the GetMaxCharCount method generally executes faster.
GetMaxCharCount is a worst-case number, including the worst case for the currently selected DecoderFallback. If a fallback is chosen with a potentially large string, GetMaxCharCount can return large values.
In most cases, this method returns reasonable numbers for small strings. For large strings, you might have to choose between using very large buffers and catching errors in the rare case that a more reasonable buffer is exceeded. You might also want to consider a different approach and use GetCharCount or Convert.
GetMaxCharCount has no relationship to GetBytes. If you need a similar function to use with GetBytes, use GetMaxByteCount.
Anteckning
GetMaxCharCount(N) is not necessarily the same value as N* GetMaxCharCount(1).
| Produkt | Versioner |
|---|---|
| .NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9, 10 |
| .NET Framework | 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
| .NET Standard | 1.3, 1.4, 1.6, 2.0, 2.1 |
| UWP | 10.0 |
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